Halftoning is a process by which continuous tone images are approximated by a pattern of pixels that can achieve only a limited number of discrete intensities. An example of this is the rendering of gray tones with black and white pixels, such as in a newspaper photograph. A halftone pattern is made up of a region of pixels referred to as a halftone cell. In conventional digital halftoning (e.g., halftoning that uses rational tangent angles), a halftone cell includes a specific, repeatable pattern. The discrete number of tonal levels of a halftone pattern depends upon the number of pixels in the halftone cell and the number of exposure levels or dot sizes for each pixel.
Halftones yield different optical densities on different paper types, depending on paper characteristics (e.g., coating, pulp, and chemicals used in the manufacturing process). Thus, using an ink jet printer for the same amount of ink at each gray level, the resultant optical densities may be different for each paper type. High speed production printer facilities use a variety of papers to accommodate print jobs. In some instances, the same print job may need to be printed on different paper at different print sites, with the objective of the visual appearance of the jobs to be the same. Such an objective may prove difficult in cases where custom color profiles are not used and device color printing is employed.
Because the same halftones are typically used in the above-described instance, a different appearance is produced for different paper types. Thus, calibration is performed to achieve desired results. However, conventional calibration approaches require a significant number of measurements.
Accordingly, an improved halftone calibration mechanism is desired.